Refactor API response structure to use 'body' instead of 'data' for consistency across all endpoints. Update stub responses and documentation accordingly.

stubs/api/index.js

@@ -11,14 +11,15 @@ const loadJSON = (filename) => {
   return JSON.parse(data);
 };
 
-const respond = (res, data) => {
-  res.json({ error: null, data });
+const respond = (res, body) => {
+  res.json({ success: true, body });
 };
 
 const respondError = (res, message, statusCode = 400) => {
   res.status(statusCode).json({ 
-    error: { message }, 
-    data: null 
+    success: false,
+    body: null,
+    error: { message }
   });
 };